My understanding is that cognition encompasses verbal skills, comprehension etc in the context of developmental norms, given that cognitive abilities DO change a lot within this 5-12 age block anyway. It's still to do with how kids learn and what may impede learning progression if the teaching is delivered at a certain level of expectation. Cognition is pretty broad, whereas literacy testing is more specific and is not the kind of assessment in mind in this case.
I'm not an expert and my own kid isn't at this age yet, so I'm just demystifying what the assessment will be used for and how it should be conducted and what your rights are as the parent. It's not a scary thing, it will actually help you all